Bacterial genome diversity is largely due to bacterial viruses, such as temperate phages that can integrate and maintain into the host genome. In bacteria, although most of the prophage genes are silent, some of them are expressed and give new properties to bacteria such as stress adaptation and virulence factors. Moreover, it has been shown that expression of some prophage genes is under the control of bacterial regulators. On the contrary, proteins from phages could regulate the expression of bacterial genes.
My work illustrates this cross regulation existing between phages and bacteria. Indeed, I currently study the regulatory interplay existing between RpoS, a bacterial master regulator and AppY, a transcriptional regulator encoded by the DLP12 prophage.
RpoS is the major sigma factor during stationary phase and under many stress conditions in γ-proteobacteria. This factor controls the expression of more than 500 genes in E. coli and is itself highly regulated at different levels: transcription, translation and protein stability. Interestingly, the overproduction of AppY, a poorly studied transcriptional regulator encoded by DLP12 prophage in E. coli K12, leads to RpoS increase in the cell. Our goal is to elucidate the molecular mechanism leading to this increase in RpoS level in the presence of AppY and define the physiological conditions that could result in AppY as well as RpoS induction. On the other hand, it has been proposed that RpoS could regulate appY transcription. However, our data suggest that RpoS could influence AppY level in the cell independently of its synthesis.
Overall, our goal is to study the regulatory network existing between prophage and bacteria in order to understand how genes from foreign origin can evolve to integrate into the genome of the bacterial host.